1. Field of the Invention
The present invention relates to a display device having an element which sandwiches a light-emitting material between electrodes (hereinafter, a light-emitting element) and a method for manufacturing the same. Specifically, the invention relates to a display device using a light-emitting material from which EL (Electro Luminescence) can be obtained (hereinafter, an EL material).
2. Description of the Related Art
An EL material (particularly an organic EL material) constituting the principal part of an EL element has properties weak in moisture and tends to be deteriorated. Thus, a structure in which a desiccant is put in an EL display device (electroluminescence device) to seal is known (for example, Reference 1: Japanese Patent Laid-Open No. 2003-297558).
FIG. 2 is a conventional display device, and reference numeral 50 denotes an element substrate; 51, an element portion such as a driver circuit portion having a TFT or an element, or a pixel portion; 53, a desiccant; 54, a sealant; 55, a depression provided with the desiccant 53; and 60, a sealing substrate.
In order to provide the desiccant 53 in the conventional display device shown in FIG. 2, the sealing substrate 60 is processed to form the depression 55. This depression 55 is formed by a blast processing method, a mechanical processing method such as mill processing, a chemical processing method melting a glass substrate, or the like. The blast processing method is a processing method such as a sandblasting method by colliding abrasive grains such as sand. These methods have a problem such as dust or contamination of heavy metal in the manufacturing steps; therefore, it is required to tackle the problem by employing a cleaning method thereof or the like. In addition, since the depression is like ground glass and or has depression and projection with the use of mechanical processing or the like, the light extraction efficiency is decreased. Therefore, it is inappropriate for a top emission or dual emission type display device. Light extraction efficiency indicates the ratio of the amount of luminescence of an element emitted to the atmosphere through the top surface of a substrate, to the initial amount of luminescence of the element.
In the conventional methods, a processing step of forming a depression in a sealing substrate in such a manner is necessary and apparatus necessary for the step increases, and thus the step becomes complicated. There is possibility that a sealing substrate is damaged due to the processing step. Therefore, there is fear that light-transmitting properties of the sealing substrate is deteriorated by being roughed and by impairing the planarity or that a thin sealing substrate is damaged. In addition, it is difficult to form a depression in an element substrate as formed in the sealing substrate, and there is limitation on the place to provide a desiccant.